1. Field of the Invention
The present invention relates to a wireless power feeder and a wireless power transmission system for transmitting power by a non-contact method.
2. Related Background Art
Japanese Patent Application Publication No. 2010-22076 discloses a wireless power transmission system (contactless power transmission device) which transmits power by a non-contact method from a power feed coil (primary coil) to a power receive coil (secondary coil) utilizing an electromagnetic induction effect which is a kind of magnetic coupling (electromagnetic coupling).
In this kind of wireless power transmission system, the coupling state between the power feed coil and the power receive coil changes (e.g., mutual inductance of these coils varies) and power transmission efficiency declines due to variation of the inductance of the power feed coil and the power receive coil, change of the relative distance between the power feed coil and the power receive coil, a positional deviation of the power feed coil or the power receive coil, intrusion of foreign material between the power feed coil and the power receive coil, or the like.
In respect of this point, Japanese Patent Application Publication No. 2010-22076 describes that a means for supplying AC power or current to the power feed coil and a means for detecting the power or current supplied to the power feed coil are provided and the frequency of the AC power or current is controlled so as to maximize the power or current to be supplied to the power feed coil. By this means, decline in the power transmission efficiency can be avoided and the transmission efficiency can be improved.
Meanwhile, Japanese Patent Application Publication No. 2010-239816 discloses a wireless power transmission system which transmits power by a non-contact (wireless) method from a wireless power feeder to a wireless power receiver utilizing a magnetic field resonance effect which is a kind of magnetic coupling (electromagnetic coupling). In this wireless power transmission system, a wireless power feeder is provided with a power feed resonance circuit including a power feed coil and stray capacitance and a wireless power receiver is also provided with a power receive resonance circuit including a power receive coil and stray capacitance.
Also in this kind of wireless power transmission system, the coupling state between the power feed resonance circuit and the power receive resonance circuit changes (e.g., resonance frequencies of these resonance circuits shift or mutual inductance between these coils varies) and power transmission efficiency declines due to variation in a quality of components constituting each of the power feed resonance circuit and the power receive resonance circuit, change of the relative distance between the power feed coil and the power receive coil, a positional deviation of the power feed coil or the power receive coil, intrusion of foreign material between the power feed coil and the power receive coil, or the like.
In this regard, also in a wireless power transmission system disclosed in Japanese Patent Application Publication No. 2010-239816, it is expected to be able to avoid the decline of the power transmission efficiency and to improve the transmission efficiency by controlling the frequency of AC power or current to be supplied to the power feed coil in the power feed resonance circuit.
Incidentally, when power transmission is being continued in a case in which the power transmission efficiency declines due to the variation in quality of components constituting each of the power feed resonance circuit and the power receive resonance circuit, due to the change of the relative distance between the power feed coil and the power receive coil, due to the positional deviation of the power feed coil or the power receive coil, due to the intrusion of foreign material between the power feed coil and the power receive coil, or the like, there is a risk that loss in the transmitting and receiving system and unnecessary radiation increase and some sort of failure occurs due to these hazardous factors.
In this regard, Japanese Patent Application Publication No. 2010-239816 describes that a frequency profile when the frequency of the AC power or current to be supplied to the power feed coil in the power feed resonance circuit is changed in a predetermined range, that is, a frequency profile showing a frequency dependence of a power transmission state is obtained, and then the obtained frequency profile is compared with a preliminarily measured normal frequency profile, and power transmission should be stopped if the obtained frequency profile does not match the normal frequency profile. By this means, occurrence of the failure due to the decline of the power transmission efficiency can be avoided.